1. Field of the Invention
The invention disclosed herein relates to energy storage cells, and in particular to advanced electrolyte systems for use in these energy storage cells, and related techniques for providing an electric double-layer capacitor that is operable at high temperatures.
2. Description of the Related Art
Energy storage cells are ubiquitous in our society. While most people recognize an energy storage cell simply as a “battery,” other types of cells should also be included within this context. For example, recently, ultracapacitors have garnered much attention as a result of their favorable characteristics. In short, many types of energy storage cells are known and in use today.
An electric double-layer capacitor, also known as a “supercapacitor,” “supercondenser,” “pseudocapacitor,” “electrochemical double layer capacitor,” or “ultracapacitor,” is a capacitor that exhibits substantially improved performance over common capacitors. One such parameter is energy density. Generally, an ultracapacitor has an energy density that is on the order of thousands of times greater than a high capacity electrolytic capacitor.
Capacitors are one of the key components in any electronic device and system. Traditional functions include power supply voltage smoothing, supporting the energy source, and filtering. A variety of industries present demanding environments for implementation of electronics and capacitors.
Consider, for example, that industries such as oil-drilling, aerospace, aviation, military and automotive have some applications that require electrical components to work continuously at high temperatures (for example, at temperatures in excess of eighty degrees Celsius). This heat exposure, along with a variety of factors, work to degrade performance of energy storage systems at elevated temperatures, and lead to premature degradation of the energy storage cell. Durability and safety are key requirements in typical aerospace and defense applications. Applications such as those where engines, turbo fans, and control and sensing electronics are placed near outer shells of a rocket engine. Automotive applications, such as small gearboxes or embedded alternators/starters, also require durability and long life at elevated temperatures.
Electronic components used in industrial environments must be physically robust while meeting demands for performance. For designers and producers of ultracapacitors, one of the attendant challenges is obtaining an electrolyte that will function well and reliably at high temperatures, as well as one that will function well and reliably at both high temperatures and low temperatures. Unfortunately, the desirable properties of some electrolytes are not exhibited or sustained at higher temperatures, and even those that have achieved durability at high temperatures have not been able to serve as reliably at lower temperatures. Thus, what are needed are electrolytes for ultracapacitors that perform well in demanding situations. Preferably, the electrolytes provide stable conductivity and low internal resistance as well as stable and high capacitance, and stable and low leakage current over a wide range of temperatures.